The present invention relates to methods for preparing a polybutadiene latex. More particularly, the present invention relates to methods for preparing a polybutadiene latex, which can reduce reaction times in polymerization of butadiene and agglomeration of polybutadiene when a polybutadiene latex is produced.
Also, the present invention includes an agglomerating agent for effectively agglomerating polybutadiene latices, and methods for preparing the agglomerating agent.
In general, rubbery latex is used in preparation of impact-resistant resin compositions for improving impact strength thereof. An agglomerating agent is used for preparing the rubbery latex. Various methods for agglomerating rubbery latices have been employed up to now.
For example, in preparation of ABS resin which is impact-resistant, the resin is prepared by agglomerating polybutadiene rubber particles with an agglomerating agent, graft-polymerizing monomers of styrene and acrylonitrile onto the polybutadiene latex, and mixing the grafted polymer and SAN (styrene-acrylonitrile) copolymer.
In an impact-resistant resin, particle sizes of rubbery latex affects impact-strength of a molded article of the resin, as well as other physical properties thereof.
Generally, it is preferable that the particle sizes of the rubbery latex are in the range of 0.25xcx9c1.0 xcexcm. For preparing the rubbery latex having particle sizes of 0.25xcx9c1.0 xcexcm, there have been various researches on agglomerating agents, methods for preparing the agents, and methods for agglomerating rubbery latices.
Japanese Patent Publication No. 56-45921 discloses a method for increasing particle size of synthetic rubbery latex using a latex that is polymerized from 97xcx9c70% by weight of an alkyl acrylate of C1xcx9cC12 and 3xcx9c30% by weight of an unsaturated acid in the presence of an anionic surfactant.
Japanese Patent Laid-open No. 58-61102 discloses a latex as agglomerating agent which is prepared by emulsion-polymerization of an unsaturated acid, an alkyl acrylate, and monomers polymerizable therewith, and a method for preparing the latex.
Japanese Patent Publication No. 1-32842 discloses a latex as agglomerating agent which is prepared by emulsion-polymerization of an unsaturated acid, diene monomers, and monomers polymerizable therewith, and a method for preparing the latex.
U.S. Pat. No. 3,049,500 teaches a method of increasing the size of the polymer particles in a synthetic rubber latex of a copolymer of butadiene-1,3 and styrene which comprises incorporating in the latex of polyvinyl methyl ether and an alkali salt electrolyte.
U.S. Pat. No. 3,330,795 teaches a latex consisting essentially of a mixture of a synthetic rubber dispersion and an oxidized polyalkylene oxide having a molecular weight within the range from 3,000 to 30,000 and a substantial xe2x80x94Cxe2x95x90O group content of not more than 8%.
U.S. Pat. No. 3,403,125 discloses a method for agglomerating a rubber latex using an agglomerating agent obtained by reacting a polyoxyethylene glycol with the diepoxide obtained by condensing epichlorohydrin with a polyhydric (alcohol) phenol.
European Publication No. 0029613 A1 discloses an agglomerating latex containing (1) a polymer selected from (a) homopolymers of alkyl acrylates and methacrylates in which the alkyl has from 1 to 12 carbon atoms, and (b) copolymers of ethylenically unsaturated monomers capable of forming water insoluble homopolymers, and (2) a non-ionic surfactant consisting of an addition product of ethylene oxide.
European Publication No. 0143858 A1 discloses an agglomerating agent copolymer having an elastomeric xe2x80x9ccorexe2x80x9d and grafted thereto a xe2x80x9cshellxe2x80x9d of interpolymer comprising polymerized acid and ester comonomers.
European Publication No. 0406806 A2 discloses an agglomerated rubber copolymer prepared by emulsion-polymerizing an alkyl acrylate/1,3-butadiene mixture, and then agglomerating the resulting rubbery copolymer. The agglomeration is effected by adding (a) an acid group-containing copolymer prepared by emulsion polymerizing an alkyl methacrylate/unsaturated monomer mixture, and (b) an oxy acid salt selected from alkali metal, alkaline earth metal, zinc, nickel, and aluminum salts of oxy acids.
When an alkyl acrylate is used as an agglomerating agent of a rubber latex, a semi-batch type is employed due to a severely exothermic reaction of the alkyl acrylate. This process has an advantage in removal of exothermic heat. However, the process does not form uniform cores, and provides latex particles having a large distribution of particle size.
When an ionic comonomer is used in the preparation of an agglomerating agent for agglomerating rubber latex, the ionic comonomer should exist at the surface of the agglomerating agent to be prepared, thus having a high agglomeration effect. According to conventional methods for preparing an agglomerating agent, the ionic comonomer exists inside the agglomerating agent, but not at the surface of the agent.
The present inventors developed an agglomerating agent which can effectively agglomerate rubber latex by reducing reaction times of agglomeration.
U.S. Pat. No. 5,294,659 teaches a method for emulsion polymerization of butadiene in an emulsion polymerization medium, comprising providing an emulsion polymerization medium containing monomer consisting essentially of butadiene and up to about 50% by weight of an aryl olefin comonomer, and a soap, and adding an acrylic latex to the emulsion polymerization medium during the polymerization.
Korean Patent Publication No. 94xcx9c10341 teaches a method for preparing rubber latex having increased particle sizes by adding 0.1xcx9c10 parts by weight of a latex for controlling particle size, comprising diene monomers and aqueous monomers capable of agglomerating polymers, at the time of polymerization conversion rate of 80%. And, Korean Patent Publication No. 96-854 discloses a method for preparing a latex having an increased particle size, a high solids content and a high glass transition temperature, comprising reacting an aryl olefin compound or alkyl methacrylate compound with/without a vinyl cyanide compound in the presence of an emulsion polymerization medium, and adding 0.1xcx9c10 parts by weight of a controlling agent of particle size to the emulsion polymerization medium when the polymerization conversion rate reaches to 5xcx9c50%.
Considering the reaction temperature and solids content of a rubber latex, conventional methods cannot produce rubber latex having an increased particle size. Particularly, when a certain solids content of rubber latex is to obtain, the reaction times are long, which is uneconomical in the production of rubber latex.
In accordance with the present invention, the inventors provide methods for preparing rubber latex having an increased particle size at a certain reaction temperature and solids content, and for reducing reaction times, thereby improving productivity of rubber latex.
An object of this invention is to provide methods for preparing a polybutadiene latex, which can shorten reaction times in polymerization of butadiene and agglomeration of polybutadiene when a polybutadiene latex is produced.
Another object of the invention is to provide methods for preparing rubber latex having an increased particle size at a certain reaction temperature and solids content.
A further object of the invention is to provide methods for preparing rubber latex for improving productivity thereof by shortening reaction times in polymerization of butadiene and agglomeration of polybutadiene.
A further object of the invention is to provide a polybutadiene latex that can provide a good impact strength, when the latex is applied to an impact-resistant resin composition.
A further object of the invention is to provide an agglomerating agent that ionic comonomers polymerized with alkyl acrylate exist at the surface of the agglomerating agent to be prepared in a sufficient amount, thus having a high agglomeration effect.
A still further object of the invention is to provide methods for preparing an agglomerating agent that ionic comonomers polymerized with alkyl acrylate exist at the surface of the agglomerating agent to be prepared in a sufficient amount, thus having a high agglomeration effect.
These and additional objects can be achieved by the resin compositions according to the present invention.
In accordance with the present invention, the method for preparing a polybutadiene latex comprises providing an emulsion polymerization medium by reacting a mixture of water, butadiene monomers, a surfactant, a chain transfer agent, an initiator and an electrolyte, preferably at a temperature of about 60xcx9c80xc2x0 C. for about 8xcx9c16 hours, whereby a conversion rate being 80xcx9c100%, a solids content of the polymerized latex being about 35xcx9c45%, and a particle size being 1000xcx9c3500 xc3x85, and agglomerating the resulting emulsion polymerization medium at a temperature of 5xcx9c20xc2x0 C. higher than the polymerization temperature for 4xcx9c12 hours by adding a surfactant and an agglomerating agent to the emulsion polymerization medium in a consecutive order, whereby the particle size of the final polybutadiene latex is in the range of 3000xcx9c15000 xc3x85.
In this invention, a surfactant is used in the amount of 0.5xcx9c3.0 parts by weight in the polymerization step, and in the amount of 0.1xcx9c2.5 parts by weight in the agglomeration step, per 100 parts by weight of butadiene monomers.
In the polymerization step, a chain transfer agent of 0.3xcx9c1.0 parts by weight and an electrolyte of 0.3xcx9c1.5 parts by weight are used per 100 parts by weight of butadiene monomers.
In the agglomeration step, an agglomerating agent of 0.1xcx9c5.0 parts by weight is used per 100 parts by weight of butadiene monomers.
In accordance with the present invention, the polybutadiene latex can be prepared within 12xcx9c28 hours, thereby shortening preparation times, and expected to have a good impact strength, when the latex is applied to an impact-resistant resin composition, because coagulum is not formed.
An agglomerating agent of this invention is prepared with an alkyl acrylate, an ionic comonomer, an anionic surfactant and an anionic initiator.
The method for preparing the agglomerating agent comprises a first step of forming agglomerating seeds by batch polymerization of an alkyl acrylate of C1xcx9cC12, an anionic surfactant and an anionic initiator, thereby conversion rate being more than 90%, a second step of growing the agglomerating agent in semi-batch polymerization by adding an alkyl acrylate of C1xcx9cC12 and an ionic comonomer to the resulting polymer of the first step, and a third step of copolymerizing the ionic comonomer at the surface of the agglomerating agent to be prepared in a sufficient amount, by adding an alkyl acrylate of C1xcx9cC12, an ionic comonomer and an anionic initiator to the resulting polymer of the second step, thus having a high agglomeration effect.
The agglomerating agent of this invention composes of 0.1xcx9c0.5 parts by weight of an ionic comonomer, 0.5xcx9c4.0 parts by weight of an anionic surfactant, and 0.3xcx9c2.0 parts by weight of an anionic initiator, per 100 parts by weight of alkyl acrylate. For the total alkyl acrylate to be used, 5% or less by weight is used in the first step, about 90% by weight is used in the second step, and the remaining alkyl acrylate is used in the third step. For the total ionic comonomer to be used, 5xcx9c20% by weight is used in the second step, and 80xcx9c95% by weight is used in the third step. For the total anionic initiator to be used, 90xcx9c70% by weight is used in the first step, and 10xcx9c30% by weight is used in the third step.
In accordance with the present invention, the method for preparing a polybutadiene latex comprises a polymerization step for providing an emulsion polymerization medium of butadiene, and an agglomeration step for agglomerating the polybutadiene latex which has been prepared in the polymerization step.
The polymerization step is carried out in conventional emulsion polymerizations by reacting water, butadiene monomers, a surfactant, a chain transfer agent, an initiator and an electrolyte at a temperature of 60xcx9c80xc2x0 C. for 8xcx9c16 hours, whereby a conversion rate being 80xcx9c100%. The butadiene monomers are added so that a solids content of the polymerized latex may be 35xcx9c45%. In a polymerization of polybutadiene latex, the higher the solids content of the latex is, the longer the polymerization time is. Accordingly, it is preferable that the solids content of the polymerized latex is in the range of 35xcx9c45% in this invention. Also, it is preferable that the particle size of polybutadiene latex is in the range of 1000xcx9c3500 xc3x85.
Representative examples of a surfactant to be used in this invention are sodium laurylsulfate, potassium oleate and rosin soap, which are used in an aqueous state. In the polymerization step, a surfactant is used in the amount of 0.5xcx9c3.0 parts by weight per 100 parts by weight of butadiene monomers. The surfactant is used also in the agglomeration step following the polymerization step. The function of the surfactant in the polymerization step is to form a primary particle size of polybutadiene latex, and the function of the surfactant in the agglomeration step is to provide stability of polybutadiene latex.
Illustrative examples of a chain transfer agent usable in this invention are tert-dodecyl mercaptan, methyl mercaptan, and tert-butyl mercaptan. In the polymerization step, a chain transfer agent is preferably used in the amount of 0.3xcx9c1.0 parts by weight per 100 parts by weight of butadiene monomers. If the chain transfer agent is used in excess of the amount or less than the amount, the polybutadiene latex cannot have a good particle shape when they agglomerate, and it is difficult to control the particle shape of the latex in the polymerization of acrylonitrile-butadiene-styrene.
Representative examples of an electrolyte to be used in this invention are calcium carbonate, sodium bicarbonate, and tricalcium phosphate. In the polymerization step, an electrolyte is used in the amount of 0.3xcx9c1.5 parts by weight per 100 parts by weight of butadiene monomers. The amount of an electrolyte can control the particle size and distribution of particle size of polybutadiene latex, and provide stability of polybutadiene latex.
After adding water, butadiene monomers, a surfactant, a chain transfer agent, and an electrolyte, the reaction temperature will be increased to 60xcx9c80xc2x0 C. for emulsion polymerization. The temperature is reached, polymerization is carried out by adding an initiator such as potassium persulfate to the reactor. Use of an initiator will be apparent to an ordinary skilled person in the art. The polymerization should be carried out for 8xcx9c16 hours so that a conversion rate may be 80xcx9c100%, thereby a solids content of polybutadiene latex being 35xcx9c45%, and a particle size being 1000xcx9c3500 xc3x85.
When the polymerization step has been completed, agglomeration step is proceeded. An agglomerating agent and a surfactant are added to the emulsion polymerization medium. After raising the reaction temperature 5xcx9c20xc2x0 C. higher than that of polymerization step, polybutadiene latex is agglomerated for 4xcx9c12 hours.
The agglomerating agent to be used in the agglomeration step composes of an alkyl acrylate, an ionic comonomer, an anionic surfactant and an anionic initiator.
The agglomerating agent is prepared by a method comprising a first step of forming agglomerating seeds by batch polymerization of an alkyl acrylate of C1xcx9cC12, an anionic surfactant and an anionic initiator, thereby conversion rate being more than 90%, a second step of growing the agglomerating agent in semi-batch polymerization by adding an alkyl acrylate of C1xcx9cC12 and an ionic comonomer to the resulting polymer of the first step, and a third step of copolymerizing the ionic comonomer at the surface of the agglomerating agent to be prepared in a sufficient amount, by adding an alkyl acrylate of C1xcx9cC12, an ionic comonomer and an anionic initiator to the resulting polymer of the second step, thus having a high agglomeration effect.
The agglomerating agent of this invention composes of 0.1xcx9c0.5 parts by weight of an ionic comonomer, 0.5xcx9c4.0 parts by weight of an anionic surfactant, and 0.3xcx9c2.0 parts by weight of an anionic initiator, per 100 parts by weight of alkyl acrylate. For the total alkyl acrylate to be used, 5% or less by weight is used in the first step, about 90% by weight is used in the second step, and the remaining alkyl acrylate is used in the third step. For the total ionic comonomer to be used, 5xcx9c20% by weight is used in the second step, and 80xcx9c95% by weight is used in the third step. For the total anionic initiator to be used, 90xcx9c70% by weight is used in the first step, and 10xcx9c30% by weight is used in the third step.
In the first step, seeds of agglomerating agent are formed by batch polymerization of alkyl an acrylate, an anionic surfactant and an anionic initiator. It is preferable that conversion rate should be more than 90%. An anionic surfactant of 0.5xcx9c4.0 parts by weight per 100 parts of the total alkyl acrylate may be used in the first step. For the total alkyl acrylate to be used in the preparation of the agglomerating agent, 5% or less by weight is used in the first step. This amount of alkyl acrylate in the first step can form seeds of agglomerating agent, and prevent enlarging distribution of particle size of the agent, thereby preparing uniform particle size of the agent. An anionic initiator of 0.3xcx9c2.0 parts by weight per 100 parts of the total alkyl acrylate may be used in the first step. For the total anionic initiator to be used, 90xcx9c70% by weight is used in the first step.
In the second step, the agglomerating agent is grown in semi-batch polymerization by adding an alkyl acrylate of C1xcx9cC12 and an ionic comonomer to the resulting polymer of the first step.
The ionic comonomer is a functional monomer which exists at the surface of the agglomerating agent. For the total alkyl acrylate to be used, about 90% by weight is used in the second step. An ionic comonomer is used in the amount of 0.1xcx9c0.5 parts by weight per 100 parts of alkyl acrylate. Among them, 5xcx9c20% by weight of an anionic comonomer is used in the second step. The second step is to grow particle size of agglomerating agent. In this step, addition rate of monomers should be controlled so as to balance the equivalence between exothermic heat from the polymerization of alkyl acrylate and radiation heat to the outside system. The semi-batch polymerization can be easily carried out by an ordinary skilled person in the art.
In the third step, an alkyl acrylate of C1xcx9cC12, an ionic comonomer and an anionic initiator are added to the resulting polymer of the second step, and the ionic comonomer is copolymerized at the surface of the agglomerating agent to be prepared, thus having a high agglomeration effect. It is preferable that conversion rate should be more than 95%.
Among the total amount of alkyl acrylate used in the three steps, 5% by weight of alkyl acrylate is used in the third step, and 95% by weight is used in the first and second steps. Among the total amount of ionic comonomer to be used, 80xcx9c95% by weight of an ionic comonomer is used in the third step. Among the total amount of anionic initiator to be used, 10xcx9c30% by weight of an anionic initiator is used in the third step. The reason why a high portion of an ionic comonomer is employed in the third step is that more ionic comonomers are copolymerized at the surface of the agglomerating agent to be prepared, thus having a high agglomeration effect. An anionic initiator is added after ionic comonomers are sufficiently impregnated into the agglomerating agent.
This addition of an anionic initiator helps the ionic comonomers or other remaining monomers to be copolymerized at the surface of the agglomerating agent.
Alkyl acrylates of from 1 to 12 carbon atoms may be used for preparing an agglomerating agent of the invention, and butyl acrylate can be preferably used.
An ionic comonomer of this invention is a functional monomer which exists at the surface of the agglomerating agent. Unsaturated carboxylic acids and acrylic amides are used as ionic comonomer. Illustrative examples of unsaturated carboxylic acids are methacrylic acid, acrylic acid, itaconic acid, chrotonic acid, and maleic anhydride, and those of acrylic amides are acryl amide, methacryl amide, ethacryl amide, and n-butylacryl amide.
Representative examples of an anionic surfactant usable in this invention are disodium alkyl sulfosuccinate, disodium ethoxylated nonylphenol, sodium lauryl sulfate, and potassium oleate.
Representative examples of an anionic initiator usable in this invention are potassium carbonate, ammonium bicarbonate, and ammonium carbonate.
It is preferable that the average particle size of agglomerating agent of this invention is in the range of 0.05xcx9c0.2 xcexcm. Polybutadiene latex is agglomerated using this agglomerating agent. An agglomerating agent of 0.1xcx9c5.0 parts by weight per 100 parts by weight of polybutadiene latex may be used for agglomeration.
As mentioned above, when the polymerization step has been completed, an agglomeration step is proceeded using the agglomerating agent of this invention. An agglomerating agent and a surfactant are added to the emulsion polymerization medium, when conversion rate reaches to 80xcx9c100%. A surfactant of 0.1xcx9c5.0 parts by weight per 100 parts by weight of butadiene monomer is used in this step. After raising the reaction temperature 5xcx9c20xc2x0 C. higher than that of polymerization step, polybutadiene latex is agglomerated for 4xcx9c12 hours.
If polybutadiene latex is agglomerated using this agglomerating agent, it is preferable that the average particle size of agglomerated polybutadiene latex is in the range of 3000xcx9c15000 xc3x85.
According to the present invention, the polymerization step has been completed in 8xcx9c16 hours, and the agglomeration step has been completed in 4xcx9c12 hours. Therefore, this invention can shorten reaction times in polymerization of butadiene and agglomeration of polybutadiene, when a polybutadiene latex is produced.
The methods for preparing polybutadiene latex according to the present invention have effects of the invention, which can provide polybutadiene latex having an increased particle size at a certain reaction temperature and solids content, and improve productivity of polybutadiene latex by shortening reaction times in polymerization of butadiene and agglomeration of polybutadiene.